Heat the olive oil in a large pot and sauté the celery, onion, and carrot until soft, about 4 minutes. Add the garlic, cumin, and chilli, then fry for another minute.
Add all remaining ingredients except the sweet potato. Season well and bring to a simmer.
Cook for 45 minutes, stirring occasionally, then add the sweet potato. Continue cooking for another 30-45 minutes until the sweet potato is tender and the chili has thickened.
Serve with your choice of toppings.